Housings that have to accommodate electrical equipment and must be operated in potentially explosive atmospheres have to meet requirements. These requirements define the explosion-proof maximum and minimum housing permissible temperatures. The minimum housing temperature is established because the strength properties of the materials of the housing change with decreasing temperature. Below certain temperatures, for example, below −60° C., the strength of an aluminum housing is no longer sufficient to withstand explosions inside the housing.
Furthermore, the gas quantity inside the housing increases with decreasing temperature. The increased gas quantity increases the gas pressure if an explosion occurs inside the housing which can cause the housing to burst.
In addition, surfaces exposed to potentially explosive substances are potential ignition sources. The ignition hazard originating from them is influenced by the ignition temperature of the potentially explosive substance and the surface temperature. The maximum permissible temperature is determined as a function of the potentially explosive environment for which the housing is configured. The functional aspect includes the compliance with the specified temperatures for use of the components.
The maximum housing temperature is less a question of the housing material or the gas quantity, but it is more a question of heat removal outward from the electrical equipment inside the housing through the housing wall. Unless special cooling means are provided, the electrical equipment inside the housing is only cooled by the convection or heat conduction to the housing walls. If the housing walls have an excessively high temperature, there is a risk of the contained electrical equipment becoming hotter than admissible. They themselves could overheat, or ignitable gas surrounding the housing or the components could be ignited.